Background and Aim: Although antibiotics are used in the treatment of infectious diseases, there are many problems such as adverse drug reactions and resistance to antibiotics. Plants, which may have less adverse reactions, can be a suitable substitute for chemical drugs. Cichorium intybus L. is one of the herbs that can be easily found in many areas of Iran. Since Cichorium intybus L. has antimicrobial effect we can use it in the treatment of infectious diseases.Materials and Methods: This experimental study was carried out to determine the antimicrobial effect of Cichorium intybus L, on Staphylococcus aureus, E.coli, Proteus, klebsiella and Pseudomonas, compared with that of Gentamicin, and Cephalexin. Staphylococcus aureus was cultured on blood-agar medium and other microorganisms were cultured on Muller-Hilton medium. After providing the alcoholic extract of Cichorium intybus L., it was added to the culture medium ofmicroorganisms. This process was made 15 times. Then Gentamicin and Cephalexin disks were set on the culture medium of microorganisms. This process was made 6 times. After that the inhibition zone of these microorganisms was measured. The data were analyzed by using Mann-Whitney and

Kruskal-Wallis tests.

Results: Cichorium intybus L. had an antimicrobial effect on Staphylococcus aureus but the effect was less than that of Gentamicin and Cephalexin. Gentamicin had antimicrobial effect on Staphylococcus aureus, Proteus, E.coli and klebsiella but it had no effect on pseudomonas. Cephalexin had antimicrobial effect on Staphylococcus aureus, Proteus, E.coli and Klebsiella but it had no effect on Pseudomonas.

Conclusion: Cichorium intybus L. has antimicrobial effect on Staphylococcus aureus, which is a gram-positive bacterium. We conclude that perhaps Cichorium intybus L. has only antimicrobial effect on gram positive bacteria, an issue requiring more studies to prove.